Rotations of Ferroelectric Liquid Crystals
at the Air/Water Interface
Patrycja Nitoń, Andrzej Żywociński, Krzysztof
Noworyta and Robert Hołyst
study four different ferroelectric liquid crystals in Langmuir monolayers on
water surface. Only two of them exhibit the collective rotations induced by
evaporation of water through the monolayer, described for the first time by Y.
Tabe and H. Yokoyama (Nat. Mater. 2003, 2, 806). Each of these two compounds have a polar group
(which in Langmuir film is attached to water surface) and a chiral group at the
opposite ends of the elongated molecules. The other two ferroelectrics have
both groups at close proximity and therefore the chiral group is also attached
to or even submerged in water. We demonstrate that the system is able to
perform the collective molecular rotations only when the chiral group of the
strongly polar liquid-crystalline molecule in the Langmuir monolayer is not
attached to the interface and stays in the air strongly tilted. Because of a
phase shift of rotation the stripe textures with rotating director can be
created. The isotherms of surface pressure vs. molecular area of four compounds
were measured with simultaneous observations with the aid of Brewster angle microscope.
Clip 1. The movie shows the collective rotation of molecules
of compound C at 23°C on water surface. The images were taken with time
delay 2 seconds and rotation is 5 times faster than in reality.
Figure 1. Examples of the textures of rotating phases most
frequently observed in compounds B and C at the water/air
interface. The images show the areas (2.08 × 1.00) mm2.
Figure 2. Schematic drawing of the molecular organization at the
water/air interface for particular compounds in different phases.
Figure 3. Sequence of the images taken with time delay 2 s
showing a frequency of molecular rotation in compound C; the areas
denoted as 1 and 2 in image (a) rotate at different frequencies; white bar of
length 200 μm on
image (a) shows the scale.
Milczarczyk-Piwowarczyk, A. Żywociński, K. Noworyta, R. Hołyst, Collective
Rotations of Ferroelectric Liquid Crystals at the Air/Water Interface Langmuir 2008, 24
(21), pp 12354–12363